This invention relates to a dry toner for developing electrostatic images in electrophotography, electrostatic recording and electrostatic printing. More specifically, the present invention is directed to a dry toner used in full color or monochromatic copying machines, full color or monochromatic laser printers, full color or monochromatic facsimile machines and the like image forming machines.
Dry toner for use in the above image forming machines are desired to have the following characteristics:
(1) Freedom of Hot Offset:
xe2x80x9cHot offsetxe2x80x9d is a phenomenon occurring in fixation of toner image on paper with a heated roll and refers to deposition of fused toner onto the heated roll. Conventionally, an oil is applied to a heated roll to improve releasability. This requires an oil tank and hinders compactness of the apparatus. Recent trend is toward incorporation of a wax into the toner.
(2) Capability of Fixing at Low Temperature:
For reasons of energy saving, it is desired that the toner image be sufficiently fixed at a low temperature.
(3) Freedom of Toner Filming:
xe2x80x9cFilmingxe2x80x9d is a phenomenon occurring when a wax is incorporated into dry toner to improve releasability thereof from a heated roll and refers to transference of the wax to a photoconductor or carrier particles to form a film thereon.
(3) Good Fluidity:
Toner is desired to have a small particle size for obtaining high grade toner images. However, fine toner particles generally have random shapes and fail to exhibit good fluidity. Good fluidity of toner is desired to increase the amount thereof chargeable in a toner bottle and to reduce the amount of a fluidizing agent.
(4) Good Transferability:
Toner image on a photoconductor must be transferred to a transfer medium with high efficiency to obtain high quality image.
Known toner, however, fails to simultaneously attain the above characteristics. For example, to attain low temperature fixation and anti-hot offset, JP-A-S57-109825 proposes the use of a polyester partially crosslinked with a polyfunctional monomer as a toner binder and JP-B-H07-101318 proposes the use of an urethane-modified polyester as a toner binder. These toners, however, do not exhibit satisfactory fluidity and transferability.
JP-A-H07-56390 proposes a toner containing polyester particles and wax particles to reduce the amount of a silicone oil which is applied to a heated fixing roll to prevent hot offset. The proposed toner, however, fails to attain satisfactory fluidity, transferability and low temperature fixation.
To improve fluidity and transferability, JP-A-H09-43909 proposes a toner obtained by a method in which an aqueous dispersion containing a colorant, a polar resin and a releasing agent is subjected to suspension polymerization; and JP-A-H09-34167 proposes a toner obtained by treating toner particles containing a polyester resin with an organic solvent in water. The former proposal, however, fails to attain low temperature fixation, while the latter proposal fails to improve anti-hot offset.
JP-A-H11-133666 proposes a dry toner using a urea-modified polyester resin as a toner binder. While the proposed toner gives good releasability and suitable gloss, anti-hot offset is not satisfactory.
JP-H10-207116 proposes a toner having a controlled amount of a wax exposed to the external surfaces thereof and a specific particle diameter. The proposed toner, however, causes filming of spent toner.
It is, therefore, an object of the present invention to provide a dry toner which is devoid of the drawbacks of conventional toners.
Another object of the present invention is to provide a toner which exhibits sufficient anti-hot offset, which permit low temperature fixation, which is free of toner filming problems and which has good fluidity and good transferability.
In accordance with the present invention, there is provided a toner for dry developing, comprising a colorant, a binder including a modified polyester, and wax particles dispersed in said binder, wherein that portion of said wax particles having a dispersion diameter of 0.1-3 xcexcm accounts for at least 70% by number of said wax particles.
The xe2x80x9cdispersion diameter of wax particlexe2x80x9d as used herein refers to the maximum length of a line extending between two points on the peripheral line of the TEM pattern of the particle. TEM pattern is obtained as follows. A sample toner is embedded in an epoxy resin and the embedded body is cut into a slice having a thickness of about 100 nm. The slice is dyed with ruthenium tetraoxide and a cross-sectional photograph (magnification: 10,000) is taken using a transmission electron microscope.
Other objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments of the invention to follow.